1. Field of the Invention
This invention relates to a method of immobilizing microorganisms entrapped in pellets of polyurethane, polyethylene glycol or polyacrylamide as in the activated state.
2. Description of the Prior Art
Methods of biological waste treatment include an activated sludge method. According to the activated sludge method, the microorganisms (sludge) is suspended in the waste water and the treatment is carried out as the suspended microorganisms prolixerate, and, normally, under the conditions of the BOD volume load 0.6.about.0.8 Kg-BOD/m.sup.3 per day, about 50% of the removed BOD is converted into sludge. The sludge conversion rate is calculated by a formula of the sludge production (Kg)/the removed BOD (Kg). Furthermore, according to a method of biomembrane, there are living very small animals and Protozoa. Since the very small animals and Protozoa take in the produced microorganisms as feeds, the sludge conversion rate is about 30%.
The sludge conversion rate is so high as 50% according to the activated sludge method and as 30% according to the biomembrane immobilizing method. In consequence, the surplus sludge thus produced is removed from a settling basin, dehydrated and disposed by burning, reclaiming and the like, whereby the disposal of surplus sludge needs an enormous cost.
Then, recently, there has been proposed biological waste treatment methods of immobilizing the microorganisms in the activated sludge into a polymeric carrier or an inorganic carrier. These methods include a method, wherein the microorganisms or activated sludge used in the waste water treatment is immobilized into a polymeric carrier having a large surface area and an entrappingly immobilizing method of entrapping microorganisms and the like when high polymer molecules are formed from monomer. The above-described polymeric immobilizing carrier can carry out the biological waste treatment of waste water when in contact with the waste water. According to this carrier immobilizing method, the sludge conversion rate is 10% or less, so that production of surplus sludge is low.
Now, as a carrier for immobilizing the microorganisms, there has been proposed a synthetic polymer such as polyethylene and the like. When resin, porous glass or natural substance is used as the carrier, anyone of these materials is low in toxicological properties to the microorganisms, so that reduction in activity of the immobilized microorganisms is low. However, the immobilized substance is low in physical strength and presents a disadvantage in durability.
Furthermore, as the entrappingly immobilizing method, there is conceived one, wherein monomer or prepolymer (low molecular weight polymer being soluble) having a terminal bond group or groups and having a molecular weight of approx 300 to 5000 are polymerized, and entrapped in a polymeric carrier such as polyacrylamide, epoxy resin, polystyrene, polyvinyl alcohol and the like.
However, when the microorganisms are entrappingly immobilized in polyurethane for example, the immobilized microorganisms thus obtained are very high in physical strength and satisfactory in durability. However, a solution of polyurethane prepolymer used at the time of immobilizing renders a toxic effect to the microorganisms, whereby reduction in activity of the microorganisms tends to be caused.
Similarly, when the microorganisms are immobilized into polyacrylamide resin, acrylamide monomer, a crosslinker, a polymerization initiator and the like render a toxic effect to the microorganisms, so that most of the microorganisms become extinct. Particularly, most of the weak bacteria such as nitrification bacteria become extinct, and, it takes much time to proliferate the remaining bacteria.